Avoid a first-chance exception in ConflictResolver.ResolveConflict

[KirillOsenkov]

I hit a first-chance BadImageFormatException a lot with this stack:

 	mscorlib.dll!System.Reflection.AssemblyName.GetAssemblyName Line 213	C#
 	Microsoft.Packaging.Tools.Tasks.dll!Microsoft.DotNet.Build.Tasks.FileUtilities.GetAssemblyVersion	Unknown
 	Microsoft.Packaging.Tools.Tasks.dll!Microsoft.DotNet.Build.Tasks.FileUtilities.TryGetAssemblyVersion	Unknown
 	Microsoft.Packaging.Tools.Tasks.dll!Microsoft.DotNet.Build.Tasks.ConflictItem.AssemblyVersion.get	Unknown
 	Microsoft.Packaging.Tools.Tasks.dll!Microsoft.DotNet.Build.Tasks.ConflictResolver.ResolveConflict	Unknown
>	Microsoft.Packaging.Tools.Tasks.dll!Microsoft.DotNet.Build.Tasks.ConflictResolver.ResolveConflicts	Unknown
 	Microsoft.Packaging.Tools.Tasks.dll!Microsoft.DotNet.Build.Tasks.HandlePackageFileConflicts.Execute	Unknown

This is because here we try to get the assembly version of any .dll even if it's not a managed assembly:
https:/dotnet/standard/blob/master/Microsoft.Packaging.Tools/tasks/ConflictItem.cs#L56

I recommend using this simple code to first check whether a binary even represents a managed assembly:
https:/KirillOsenkov/MetadataTools/blob/master/PEFile/IsManagedAssembly.cs

Only attempt to retrieve the assembly name after we've checked that the binary is indeed an assembly.

[ericstj]

/cc @dsplaisted this code lives in the SDK as well.
We do have a better implementation on core MSBuild: https:/dotnet/standard/blob/master/Microsoft.Packaging.Tools/tasks/FileUtilities.netstandard.cs#L23

On desktop though we just call GetAssemblyName. I suppose we could use the core implementation everywhere and it would avoid the exception.

[KirillOsenkov]

Yes, that method doesn't throw on native binaries. Please use it :)

[ericstj]

Ported to the SDK: dotnet/sdk#1215

[ericstj]

Curious what file you're hitting this on. We'd only be going down this path if you had a native file conflict in your package closure, which shouldn't be the case for most projects if they are up-to-date.

[KirillOsenkov]

Unfortunately I have no recollection of what I was doing and under what circumstances I've hit this. Sorry :)

[ericstj]

We've decided that the tradeoffs for avoiding this first chance exception aren't worth it. I've opened https:/dotnet/corefx/issues/19928 to track adding an API that can be used to do this better in the future.